What type of seat are you after?
There's the fixed back, reclining, suspension seats, light weight racing style. If you do alot offroading then suspension would be they way to go.
Have a look on poly performance or quadratec to get an idea of a style you like and a price you agree with, some come with jk seat brackets. They can range from $300 to $1000 plus per seat depending on options.
Check
http://www.infrastructure.gov.au/roa.../vsb_ncop.aspx scoll down to the seating pdf.
From memory you need approval from DOT for modification and engineers stamp unless you are upgrading to a better factory seat for the model of car. If it has side airbags already I think you may have to retain that...not fully sure, best to have a read